The present invention relates to a semiconductor light source device used in an image output device for exposing a photosensitive material to light which will emit a constant amount of light at all times because the temperature of the semiconductor light source is kept at a constant value regardless of variations in the ambient temperature.
FIG. 1 shows one example of a color image output device to which the present invention is applicable. A cylindrical drum 1 rotates about a rotary shaft 2 in the N-direction in the figure for the main scanning operation. A photosensitive material 4 is mounted on the surface of the drum 1. A head block 3 is provided which is opposed to the rotary drum 1 and which carries semiconductor light sources such as a light emitting diode which emit the three primary colors red(R), green(G) and blue(B). The head block 3 is moved in the M-direction in the figure for an auxiliary scanning operation by means of a threaded bar 5 which is threaded through the head block 3, whereby color images are formed on the photosensitive material 4.
FIG. 2 is a graph showing the relation between the electric current and the amount of light emitted from a semiconductor light source. As the temperature rises from t .degree.C. to (t+.DELTA.t) .degree.C., the amount of light emitted decreases even if the current remains constant. As the amount of light from the semiconductor light source varies depending on the temperature, the intensity of the exposed image varies correspondingly, resulting in a grave defect that the color of the finished image may become uneven in density, tone, etc.